The objective of the proposed research is to use electrophysiological methods to study the population of lumbar epaxial motor units of the rat which constitute the final common pathway of the lordosis reflex -- the stereotyped sexual posturing of the female in response to well-defined somatosensory stimulation by the male. In awake, unrestrained animals, using fine ware bipolar electrodes and in situ amplified electromyography concomitant with axial movement recording registered by a small implanted mercury strain gauge attached to the dorsal spinous processes of appropriate vertebrae, we will first determine the muscle profile of the reflex. Secondly, we will study EMG and strain gauge responses following stimuli delivered to lateral vestibular nucleus and nucleus gigantocellularis, as chronic spinal rats do not perform lordosis and the reflex depends upon the integrity of the anterolateral columns of spinal cord via which these nuclei project. Acute anesthetized preparations will be used to elucidate the interaction of multisegmental and suprasegmental inputs on the motoneuron pool of participating muscles. To accomplish this we will use a gated analog integrator to determine the size of the total population of motor axons innervating a segmental level of lateral longissimus by integrating the response of its segmental muscle nerve to supramaximal single shocks delivered to ventral root. With the same method, we will determine the number of axons contributing to the segmental muscle nerve response following stimulation of cutaneous and brainstem inputs using condition-testing paradigms. The ratio of Response (cutaneous stim.): Response (ventral root stim.) will yield the fraction of the total motoneuron pool recruited by the afferent limb of the reflex. Finally motor nerve filament recording will be used to functionally isolate single motor axons in order to examine the final common pathway for evidence of facilitation by spatial convergence of segmental and suprasegmental drives.